Conventionally, in order to control a yarn winding speed of the spindle drive type yarn winding apparatus wherein a yarn is wound onto a bobbin while the rotational speed of a spindle is controlled, the following methods have been utilized.
1. A method wherein tension in a winding yarn is controlled at a predetermined constant value by utilizing a tension meter for detecting the tension.
2. A method wherein peripheral speed of a yarn package formed by winding a yarn about a bobbin is controlled at a predetermined value by utilizing a contact roller or the like which is in contact with the peripheral surface of the wound package.
In order to increase production efficiency, the amount of a yarn in a package has been increased, and accordingly, the diameter of a wound package has also increased. When a large package is wound at a constant tension by means of the tension control method described in item 1 above, a defect called "bulge," wherein yarn located at the inner layer of a package bulges from the side of the package due to a strong winding force, occurs, and therefore, it is very difficult to adjust winding conditions including a set value of tension in the yarn at adequate conditions.
When a yarn is wound at a constant peripheral speed by means of the method 2 described above, the rotational speed of a spindle at almost completion of a full package is considerably lower than that at the beginning of winding, for example, by one third to one fourth. If a yarn is wound at a constant wind or at a constant wind ratio the traverse speed is decreased as the rotational speed of a spindle decreases. Accordingly, the winding yarn speed which can be obtained as a vector sum of the peripheral speed and the traverse speed decreases considerably. In a winding process, such as winding of a spun yarn wherein the yarn supply speed is unchanged, the decrease of the winding speed results in a decrease of tension in the yarn and deformation of a wound package due to the excessive decrease in yarn tension. In general, it is preferable to tightly wind the inner layer of a package and to loosely wind the outer layer of the package in order to prevent occurrence of bulge in a large package. However, taking other factors, such as ease of unwinding of a yarn from a package, into consideration, a suitable tension pattern by which a package can be preferably wound is different from the above-described pattern wherein the tension in the yarn is always maintained constant.